Invalidate any dependent patterns when a <pattern> is attached/detached

SVGPatternElement::CollectPatternAttributes() rejects linked <pattern>
elements that are not attached, so we need to make sure that they re-
evaluate their attributes if a referenced element gets/loses a
LayoutObject.

Bug: 1164735
Change-Id: I0f1e28c890f7f91cacbfa0f8be133d919df5c7db
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2620564Reviewed-by: Stephen Chenney <schenney@chromium.org>
Commit-Queue: Fredrik Söderquist <fs@opera.com>
Cr-Commit-Position: refs/heads/master@{#842066}

third_party/blink/renderer/core/layout/svg/layout_svg_resource_pattern.cc

@@ -60,6 +60,23 @@ void LayoutSVGResourcePattern::RemoveAllClientsFromCache() {
   MarkAllClientsForInvalidation(SVGResourceClient::kPaintInvalidation);
 }
 
+void LayoutSVGResourcePattern::WillBeDestroyed() {
+  NOT_DESTROYED();
+  To<SVGPatternElement>(*GetElement()).InvalidateDependentPatterns();
+  LayoutSVGResourcePaintServer::WillBeDestroyed();
+}
+
+void LayoutSVGResourcePattern::StyleDidChange(StyleDifference diff,
+                                              const ComputedStyle* old_style) {
+  NOT_DESTROYED();
+  LayoutSVGResourcePaintServer::StyleDidChange(diff, old_style);
+  if (old_style)
+    return;
+  // The resource has been attached, any linked <pattern> may need to
+  // re-evaluate its attributes.
+  To<SVGPatternElement>(*GetElement()).InvalidateDependentPatterns();
+}
+
 bool LayoutSVGResourcePattern::RemoveClientFromCache(
     SVGResourceClient& client) {
   NOT_DESTROYED();

third_party/blink/renderer/core/layout/svg/layout_svg_resource_pattern.h

@@ -59,6 +59,9 @@ class LayoutSVGResourcePattern final : public LayoutSVGResourcePaintServer {
   }
 
  private:
+  void WillBeDestroyed() override;
+  void StyleDidChange(StyleDifference, const ComputedStyle* old_style) override;
+
   bool FindCycleFromSelf(SVGResourcesCycleSolver&) const override;
   std::unique_ptr<PatternData> BuildPatternData(
       const FloatRect& object_bounding_box);